I use mine as a fermentation chamber/lagering chamber. I have quite a few 'shop towels' that I line the bottom of the freezer w/. I change these out after every cycle of fermentation.
The other thing I do is take up all of the dead space w/ 1 gallon water jugs. This helps regulate the temperature better by acting as a sort of insulation thereby lessening the amount of time the freezer has to run.
Like goswell says, it is tough to avoid but by doing what I've outlined above I have not had a problem w/ mold, just quite a bit of moisture. One more thing, try to limit the amount of time that the freezer is open; this allows moisture to condense inside.